The invention is directed to the separation of a mixture of two immiscible fluids of different specific gravities. In one aspect, it is directed to an apparatus for separating the two fluids by gravity and a multi-directional flow pattern. In another aspect, it is directed to a method for separating the two fluids by gravity and a multi-directional flow pattern.
Due to problems of environmental pollution, there is increased interest in the separation of oil from mixtures of oil and water. Such separations may be necessary in large bodies of water, as in the case of oil slicks on oceans and lakes caused by leakage from tankers, drilling rigs, and storage tanks, which cause serious pollution of both open water and to the shore, and consequently injury to aquatic and terrestrial fauna and flora. Similarly, oil-water mixtures resulting from industrial activities has produced serious pollution problems when discharged into rivers, streams and other bodies of water. For plants with central wastewater treatment systems, the discharge of large volumes of oily waste water is an expensive and difficult treatment burden.
For example, many machine parts or heat treated parts are washed in parts washing tanks, and the washing solution is contaminated with manufacturing oils and heat treating quench oil. In the past, this contaminated wash water has been discharged into the sewage system, but due to the resulting pollution of the water system with oil, this practice has been discontinued; as a result, it became necessary to haul the oil-contaminated wash water away to disposal sites or for further separation treatment.
Other factors engendering increased interest in the separation of mixtures of oil and water include economic considerations, and work place safety and health. Oily contamination in the parts washing solutions contributes to an inefficient cleaning process which typically requires secondary cleaning and manufacturing steps to correct. These subsequent steps present added expense and time requirements to the manufacturing process. Environmentally, the contaminating oil in parts washers is often carried into subsequent heat treating tempering furnaces where the oil burns off as smoke in the plant and smoke discharged from the plant""s smokestacks to the local environment. The health and safety of the workers is also damaged by the presence of this oily contaminant. Not only is the in-plant smoke a danger, but frequent changes of washing baths due to oil contamination require increased worker exposures to cleaning fluids and related handling hazards.
Several types of treatment methods and systems have been developed in efforts to efficiently separate oil from water-oil mixtures. One treatment method is filtration, by which oil is entrapped by a filter. Filtration may be accomplished by barrier filters, which include bag and cartridge filters, or by membrane filters, which filter fluids down to minute dimensions and are typically designed to remove emulsified oil from water. However, filters tend to clog quickly, and are time consuming and expensive to replace.
Another treatment method depends upon the use of gravity to separate a mixture of oil and water. Gravity separation exploits the difference in specific gravity between oil and water. A gravity separator typically consists of a large holding tank, in which oil rises to the surface of the water. These tanks must be substantially turbulent free to operate, and require an additional means with which to remove the oil. Thus, the tanks are filled, the oil collects at the surface and is removed, and the water returned for reuse or discharged. These tanks are slow, and require very large surface areas. Improved gravity separation involves horizontal separators. In these separators, water enters at one side of a horizontal tank, and as it flows to the other side, the oil rises to the surface, where it can be collected. The cleaner water is then discharged from another side of the tank. The oil is typically collected by means of a baffle, which holds the oil-water interface below the top of the baffle; the floating oil which accumulates above the interface then spills over the top and into a separate compartment from which it can be collected and discharged.
The use of coalescers in horizontal separators is well known. Coalescers are generally tightly packed beds of coalescing media or closely spaced plates, which aid in the separation of oil from water. Typical coalescer configurations are stacks of closely spaced plates, angled from vertical to horizontal. The plates may also be grooved or channeled, or wavy. Under the influence of gravity, oil separates from an oil/water mixture at a rate determined by Stokes law. This formula predicts how fast an object will rise or fall through a heavier fluid based on the density and size of the object and the distance it must travel. In a packed media bed coalescer, oil is exposed to large amounts of surface area provided by the coalescing media. As the oil-water mixture passes through this media, oil droplets are temporarily held by the coalescing media where they are exposed to further contact with oil molecules in the mixture. This physical contact on the surface of the coalescer media has the effect of increasing or coalescing the size of the oil droplets in the mixture. In closely spaced plate and corrugated coalescing separators oil rises only a short distance where it is captured on the underside of the coalescing plates. While the use of coalescers improves the performance of horizontal separators, the coalescers are very susceptible to clogging. In operation, these coalescing horizontal separators have the same type of failure as do filters, in that the coalescers can quickly clog and become blocked, thus requiring frequent and expensive maintenance. In addition, these coalescing separators still require a large footprint.
Another type of gravity separation is achieved by vertical separators. These separators generally involve discharge of an oil-water mixture into a vertical tube, which is generally open at the bottom and which sits in and thus empties into a water environment. This environment may be an open body of water, such as a lake or ocean, or it may be a collecting tank. The mixture is discharged near either the upper end or the lower end of the tube. As the mixture flows into the tube, the oil rises and the water sinks, effecting separation of the two different fluids. The cleaner water is discharged from the bottom of the tube into the surrounding water, whereas the oil collects at the top of the tube. The oil may be collected be means of a tube and a pump, or it may be discharged by means of an overflow tube.
A common use of such vertical separators is in off shore waste water separators. One type is a submerged caisson, which is a large diameter pipe projected vertically downward into the water and open at the bottom. A small diameter pipe is inserted vertically downward inside the large caisson to about two-thirds of its length. Oily waste water drains into the smaller interior pipe and flows downward and out into the large caisson, whereupon the flow of the water proceeds at a much lower rate, due to the larger diameter of the caisson. This allows oil droplets to separate and rise up to the surface, and the clarified water to flow down to and out the open bottom. The collected oil is allowed to accumulate until the oil-water interface is just above the inlet pipe, at which point the inflow of water is halted, and the oil pumped out. A major problem with this type of vertical separator is that the discharged, or effluent, water, still contains a considerable amount of residual oil; typically, the oil content of the water effluent is about 20% of the total initial amount of oil in the waste water.
Coalescers have also been used with vertical separators. One of the simplest is the use of gas bubbles in a pile skimmer, which is similar to the submerged caisson described above. In this system, the oily water mixture is introduced near the middle of the pipe, and gas is injected near the bottom of the pipe. The gas or dispersed gas bubbles contact and attach themselves to the oil droplets in the water, thus enhancing the gravitational separation by flotation. In another and more complex separator, a vertical tank contains a plurality of inclined corrugated plates. An oil-water mixture is introduced near the bottom of the tank, and then flows upward under pressure through the corrugated plates, which improve coalescence of the oil. The oil is directed upward by an oil channel, and the clarified water is then downward to a clean water outlet.
While these vertical separators represent improvements, they also possess distinct disadvantages. For example, open bottom cassions or skim piles do not manipulate the flow of the mixture to be separated in any way to effect physical separation between the oil and water, except by slowing down the inlet feed as it enters the separator. Due to this coarse separation mode, cassion type separators require large diameters (footprint) and large internal fluid volumes to create the separation conditions required. Thus, they are most suitable for open bodies of water; moreover, the recovered oil is not very dry, and a high percentage of the initial oil remains as residual oil in the clarified discharged water. The addition of counterflow compressed gasses requires the expense and maintenance of expensive air compressors and related equipment. These open bottom cassions or skim piles also require a substantially closed upper end to effect oil capture, which has the effect of making maintenance more difficult and making operational adjustments more difficult to visualize and calibrate accurately.
It would be very useful to provide a vertical oil-water separator which has no moving parts and which is open to the atmosphere, which is low maintenance and easy to operate, which can be operated in-line as in an industrial setting, and which has a very small footprint and is easy to install.
Thus, it is an object of the present invention to provide an apparatus for separating two immiscible fluids of differing specific gravities from a mixture of the two, where the apparatus has a small footprint, is comprised of a simple device with no moving parts, and comprises open, non clogging fluid separation passageways.
It is also an object of the present invention to provide a method for separating two immiscible fluids of differing specific gravities from a mixture of the two, where the method utilizes change if fluid flow direction and rate to effect the separation.
Surprisingly, separators of the present invention also result in the separation and collection of very high purity of both of the separated fluids. This results from the ability of the separator operators to readily check and calibrate the operation of the separator from its substantially open upper end, making it easier for operators to manipulate and control the captured fluid of lower density so as to produce a xe2x80x9cdryxe2x80x9d product substantially free of the fluid of higher density, so that the captured fluid may be resold or recycled.
Another unexpected advantage of the separators of the present invention is that they are also xe2x80x9cself-correcting,xe2x80x9d in that they are able to handle incoming mixtures of varying proportions of two different fluids, and able to handle varying flow rate of the mixture within the separator, yet still discharge the final products of each individual fluid of consistently high purity.
Thus, the invention provides a multi-directional flow gravity separator for separating a mixture of two immiscible fluids having different densities including a heavier fluid and a lighter fluid, comprising a vertical elongated tank with a first cross-sectional inner area, an upper portion, a lower portion, and an open top end, means for introducing the mixture into the tank in the upper portion such that the mixture flows downward in the tank, a vertical effluent discharge tube for discharging the heavier fluid from the lower portion of the tank, wherein the tube has a second cross-sectional inner area which is less than the first cross-sectional inner area of the tank, a lower end in fluid communication with the lower portion of the tank and an upper end in fluid communication with means for discharging the heavier fluid from the upper end of the effluent discharge tube to outside the tank, and means for discharging the lighter fluid from the upper portion of the tank. In one embodiment, the effluent discharge tube is set within the tank and further wherein the lower end is an open lower end within the lower portion of the tank. In another embodiment, the means for discharging the heavier fluid from the upper end of the fluid effluent discharge tube is a first outlet in the upper portion of the tank, and the means for discharging the lighter fluid from the upper portion of the tank comprises a second outlet in the upper portion of the tank.
The invention also provides a multi-directional flow gravity separator for separating a mixture of two immiscible fluids having different densities including a heavier fluid and a lighter fluid, comprising a vertical elongated tank with a first cross-sectional area, an upper portion, a lower portion, and an open top end, and an elongated shroud in fluid communication with the tank, wherein the shroud has a second cross-sectional inner area which is less than the first cross-sectional inner area of the tank, and an open top end and a closed bottom end, wherein the open top end is in fluid communication with the tank, an inlet pipe for introducing the mixture into the shroud, wherein the pipe has a third cross-sectional inner area which is less than the second cross-sectional inner area of the shroud and an open first end outside the tank and a second end in fluid communication with the closed bottom end of the shroud, means for discharging the heavier fluid from the lower portion of the tank, and means for discharging the lighter fluid from the upper portion of the tank. In one embodiment, the shroud is a vertical shroud and set within the tank, such that the open top end of the shroud is below the open top end of the tank and within the upper portion of the tank, and further wherein the inlet pipe is a vertical pipe within the shroud, such that the open first end is an open upper end above the open top end of the tank and where the second end is an open lower end near the closed bottom end of the shroud, such that the open lower end of the inlet pipe is in fluid communication with the closed bottom end of the shroud. In another embodiment, the means for discharging the heavier fluid from the lower portion of the tank comprises a first outlet in the lower portion of the tank, and wherein the means for discharging the lighter fluid from the upper portion of the tank comprises a second outlet in the upper portion of the tank. In yet another embodiment, the shroud further comprises a coalescer within the shroud. In yet another embodiment, the shroud and the inlet pipe are cylindrical and the shroud comprises a coalescer within the shroud, wherein the coalescer comprises a continuously spiraled vane extending from about the open lower end of the inlet pipe to about the open top end of the shroud and having an inner edge and an outer edge, wherein the inner edge of the vane is in close contact with an exterior surface of the inlet pipe, and the outer edge of the vane is in close contact with an inner surface of the shroud, such that the mixture cannot substantially pass between the outer edge of the vane and the inner surface of the shroud or between the inner edge of the vane and the exterior surface of the inlet pipe, thereby forming a helical fluid path within the shroud.
The invention also provides a multi-directional flow gravity separator for separating a mixture of two immiscible fluids having different densities including a heavier fluid and a lighter fluid, comprising a vertical elongated tank with a first cross-sectional area, an upper portion, a lower portion, and an open top end, and an elongated shroud in fluid communication with the tank, wherein the shroud has a second cross-sectional inner area which is less than the first cross-sectional inner area of the tank, and an open top end and a closed bottom end, wherein the open top end is in fluid communication with the tank, an inlet pipe for introducing the mixture into the shroud, wherein the pipe has a third cross-sectional inner area which is less than the second cross-sectional inner area of the shroud and an open first end outside the tank and a second end in fluid communication with the closed bottom end of the shroud, means for discharging the heavier fluid from the lower portion of the tank, and means for discharging the lighter fluid from the upper portion of the tank. wherein the means for discharging the heavier fluid comprises a vertical effluent discharge tube for discharging the heavier fluid from the lower portion of the tank, wherein the effluent discharge tube has a third cross-sectional inner area which is less than the first cross-sectional inner area of the tank, a lower end in fluid communication with the lower portion of the tank, and an upper end in fluid communication with means for discharging the heavier fluid from the upper end of the effluent discharge tube to outside the tank. In one embodiment, the means for discharging the lighter fluid from the upper portion of the tank comprises a first outlet in the upper portion of the tank, and wherein the means for discharging the heavier fluid from the upper end of the effluent discharge tube to outside the tank comprises a second outlet in the upper portion of the tank, such that the second outlet is slightly lower than the first outlet. In another embodiment, the effluent discharge tube is set within the tank and wherein the lower end is an open lower end within the lower portion of the tank, and further wherein the shroud is a vertical shroud and set within the tank, such that the open top end of the shroud is below the open top end of the tank and within the upper portion of the tank, and further wherein the inlet pipe is a vertical pipe within the shroud, such that the open first end is an open upper end above the open top end of the tank and where the second end is an open lower end near the closed bottom end of the shroud, such that the open lower end of the inlet pipe is in fluid communication with the closed bottom end of the shroud. In yet another embodiment, a separator further comprises a weir housing in fluid communication with the means for discharging the heavier fluid from the upper end of the effluent discharge tube to outside the tank, a weir within the weir housing and downstream of the means for discharging the heavier fluid from the upper end of the effluent discharge tube and outside the tank, and means within the weir housing and downstream of the weir for discharging the fluid from the weir housing. In yet another embodiment, the weir is an adjustable weir.
The invention also provides a separator as described previously, wherein the separator comprises a shroud and further comprises a coalescer within the shroud. In another embodiment, the shroud and the inlet pipe are cylindrical and further wherein the coalescer comprises a continuously spiraled vane extending from about the open lower end of the inlet pipe to about the open upper end of the shroud and having an inner edge and an outer edge, wherein the inner edge of the vane is in close contact with an exterior surface of the inlet pipe, and the outer edge of the vane is in close contact with an inner surface of the shroud, such that the mixture cannot substantially pass between the outer edge of the vane and the inner surface of the shroud or between the inner edge of the vane and the exterior surface of the inlet pipe, thereby forming a helical fluid path within the shroud.
The invention also provides a bi-directional flow coalescing device for separating a mixture of two immiscible fluids having different densities, comprising an elongated shroud with a first cross-sectional inner area and an open top end and a closed bottom end, an inlet pipe in fluid communication with the shroud, wherein the pipe has a second cross-sectional inner area which is less than the first cross-sectional inner area of the shroud and an open first end outside the shroud and a second end in fluid communication with the closed bottom end of the shroud, and a coalescer within the shroud. In another embodiment, the inlet pipe is a pipe within the shroud, with an open upper end above the open top end of the shroud and with an open lower end near the closed bottom end of the shroud, such that the open lower end of the inlet pipe is in fluid communication with the closed lower end of the shroud. In another embodiment, the shroud and the pipe are cylindrical and the coalescer further comprises a continuously spiraled vane extending from about the open lower end of the inlet pipe to about the open upper end of the shroud and having an inner edge and an outer edge, wherein the inner edge of the vane is in close contact with an exterior surface of the inlet pipe, and the outer edge of the vane is in close contact with an inner surface of the shroud, such that the mixture cannot substantially pass between the outer edge of the vane and the inner surface of the shroud or between the inner edge of the vane and the exterior surface of the inlet pipe, thereby forming a helical fluid path within the shroud.
The invention also provides a method for continuously separating a mixture of two immiscible fluids having different densities including a lighter fluid and a heavier fluid, where the method can be carried out by any of the embodiments described above, although it need not be limited to these embodiments.